The present invention relates to a disk storage system, such as a hard disk drive (HDD), which uses a magnetic head system in which a read head and a write head are separately mounted on a common moving arm and a disk as a storage medium, and performs an operation of reading from or writing on the disk with the heads floating so close to the disk or being in physical contact with the disk.
In order to achieve a further improvement in data recording density, magnetic head systems have been used in hard disk drives in recent years, which use a magnetoresistive (MR) head as the read head and an inductive head as the write head. In order to increase the recording density, it is effective to make the head-to-disk spacing (the flying height of the heads) small.
The magnetic heads are mounted on an air bearing slider (referred to simply as a slider.). The slider is supported by a suspension in the HDA (head/disk assembly) so that it can move across the surface of the disk while maintaining separation from the disk. The slider is formed with a surface called an ABS (air bearing surface) that is opposed to the disk surface and thus floats by the air bearing mechanism due to air flow rotating with the disk.
In order to realize a flying height that is very low, say, of the order of 30 nm, a technique has been developed which forms a protection film on the ABS and forms a protection film or a film of lubricant on the disk surface, thereby maintaining mechanical reliability even if the slider comes in contact with the disk. With such a very low flying height system or a system in which the slider surface and the disk surface are placed in contact, it becomes possible to increase the disk recording density.
With such a system, since the slider comes in contact with the disk, the degree of wear on the slider surface (ABS) or the disk surface will become large. Usually, some wear is taken into account at the time of design of HDD and such a protection film on the slider surface or disk surface as described above is a measure against wear. However, when the HDD is used in such an environment as accelerates wear (for example, an environment which receives a shock from outside), there arises a high possibility that the wear may exceed the allowable range to cause a failure in the HDD.
In particular, when the slider surface wears too much, the gap length of the write head widens, resulting in a failure to perform a write operation properly. On the other hand, since the MR element forming the read head wears when the slider surface wears, its cross-sectional area decreases. At first the resistance of the MR element will increases, leading to the increased apparent reproduction sensitivity. With an increase in the resistance of the MR element the temperature to which the MR element is heated will increase. It is known that the temperature of the MR element is proportional to the square of its resistance and the life of the MR element is exponentially proportional to the reciprocal of the temperature of the MR element. Therefore, the life of the MR element will be exponentially reduced with increasing wear. When the life of the MR element comes to an end, its reproducing capability is lost.
In the event that an error occurs in the write head, subsequent data recording will become impossible. Also, in the event that the read head does not function properly as a result of wear on the MR element, an operation of reading data retained on the disk will become impossible. In the worst case, there is the possibility that all the data retained may be lost.
For this reason, an apparatus has been proposed which is equipped with sensing means for detecting wear on the surface of a magnetic head (electromagnetic transducer) that comes in contact with the disk surface (for example, Japanese Unexamined Patent Publication No. 6-89522). The sensing means comprises two optical waveguides acting as a wear sensor on the surface of the magnetic head and optical detecting means for detecting the phase difference between laser beams reflected by the disk surface back into the optical waveguides. In that Patent Publication, sensor means is also described which comprises two resistor blocks acting as a wear sensor and electrical detecting means which detects the difference in resistance between the two resistor blocks.
That is, the system described in the Patent Publication needs to equip the HDA with additional optical or electrical means. For this reason, the arrangement of the HDA becomes complex, resulting in an increase in the manufacturing cost of the HDD.